Coating composition of non-cyclic polyanhydride and glycidyl oligomer

ABSTRACT

A coating composition with a solids content of at least about 65% by weight comprises a polyanhydride having more than one non-cyclic anhydride moiety, a glycidyl groups-containing oligomer, a catalyst and a surfactant or flow-control agent.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 08/396,458 filed Feb. 28,1995, allowed, which is a divisional application Ser. No. 08/194,785filed Feb. 10, 1994, now U.S. Pat. No. 5,428,082, which is acontinutation of application Ser. No. 07/974,569 filed Nov. 12, 1992,now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to the art of coating compositions.

It is known to apply clear and/or colored coatings to metallic and otherarticles compositions in order to improve durability and appearance,protect, finish and prevent oxidation of metals. For instance, theexterior panels of many automobiles and other outdoor articles arecoated with a multilayer finish that contains: (1) a color coat orbasecoat layer and (2) a clear coat layer. See, e.g., Blackburn et al.,U.S. Pat. No. 4,732,791 (Mar. 22, 1988), which is incorporated herein byreference.

A common coating composition contains epoxy resins and polymers whichcontain cyclic anhydrides, such as maleic anhydride and itaconicanhydride polymers and copolymers. See, e.g., Corcoran, U.S. Pat. No.4,816,500 (Mar. 28, 1989); Barsotti et al., U.S. Pat. No. 4,906,677(Mar. 6, 1990); and Schimmel, U.S. Pat. No. 4,927,868 (May 22, 1990);and Mika & Bauer, "Curing Agents and Modifiers", Epoxy Resins Chemistryand Technology, 485-92 (Marcel Dekker, Inc. 1988), which areincorporated herein by reference. Optional ingredients in thecomposition are those which are well-known in the art of formulatingsurface coatings and include surfactants, flow control agents,thixotropic agents, fillers, anti-gassing agents, organic co-solvents,catalysts and other customary auxiliaries. The components are usuallyapplied in an organic solvent and cured using a catalyst. These coatingsare frequently used in outdoor applications such as clear and colorcoating on automobiles, storage tanks, rail cars, ships, bridges,utility structures and the like.

Public concerns over the emission of volatile organic compounds havemade it desirable to coat such articles using a composition that has avery high solids content. At the same time, it is desirable for theresulting coatings to have at least about equivalent performance interms of appearance and exterior durability. What are needed are newresins that can satisfy those concerns.

SUMMARY OF THE INVENTION

One aspect of the present invention is a curable composition comprising:

(a) a polyanhydride resin that contains: (1) a central moiety, and (2)on average, more than 1 pendant non-cyclic anhydride moiety bonded toeach central moiety; and

(b) a resin that reacts with the polyanhydride resin to cure undercuring conditions.

A second aspect of the present invention is a polyanhydride thatcomprises:

(a) a polyvalent organic moiety (A);

(b) a plurality of ester linkages bonded to the polyvalent organicmoiety;

(c) divalent organic moieties (Q) bonded to the ester linkages; and

(d) non-cyclic anhydride moieties bonded to the divalent organicmoieties.

A third aspect of the present invention is a polyanhydride comprising:

(a) a central moiety which contains a polymer that has a molecularweight of at least 1000 and that contains no more than about 25 weightpercent of monomer units derived from unsaturated aliphatic hydrocarbonmonomers; and

(b) on average more than 2 pendant, non-cyclic anhydride moieties linkedto the central moiety.

A fourth aspect of the present invention is a cured composition of thepresent invention.

A fifth aspect of the present invention is a method to use a curablecomposition of the present invention, comprising the steps of:

(a) applying a coating of the curable composition to a substrate; and

(b) curing the composition applied in Step (a).

A sixth aspect of the present invention is a coated article comprising:(1) a substrate, and (2) a coating on the substrate having at least onelayer which contains a cured composition of the present invention.

The coating compositions of the present invention can be used inmixtures with relatively high solids content for coating substrates. Themixtures usually have a relatively low viscosity, and frequently have along shelf stability. The coatings have good gloss and distinctness ofimage. They may also have good chemical etch resistance and exteriordurability.

DETAILED DESCRIPTION OF THE INVENTION Coreactant Resins

Compositions of the present invention contain resins that react with thepolyanhydride to cure under a variety of conditions. Although a broadnumber of resins are useful for this purpose, the coreactant resin ispreferably an epoxy resin, a polyol resin, a polyamine or a mixturecontaining at least one of those resins. Preferred polyol resins includeacrylic polyol, hydroxy-containing polyester resins and polyhydroxypolyether resins. Preferred polyamine resins include acrylic polyamineresins and "blocked" amine resins. The most preferred coreactant resinis an epoxy resin.

Suitable coreactant coating resins are well known in the art. Examplesof suitable polyol resins are described in Shalati et al., U.S. Pat. No.4,781,806 (Oct. 3, 1989); Shalati et al., U.S. Pat. No. 5,043,220 (Aug.23, 1991); Claar et al., U.S. Pat. No. 4,798,746 (Jan. 17, 1989);Andrews et al., U.S. Pat. No. 4,826,921 (May 2, 1989); and Marrion etal., U.S. Pat. No. 4,452,948 (Jun. 5, 1984), which are incorporatedherein by reference. The molecular weight of the polyol resin ispreferably at least about 200.

Examples of suitable polyamine resins are described in Hutton et al.,U.S. Pat. No. 4,043,956 (Aug. 23, 1977); Wellner et al., U.S. Pat. No.4,279,793 (Jun. 26, 1990); Wellner et al., U.S. Pat. No. 4,970,270 (Nov.13, 1990); Wellner et al., U.S. Pat. No. 4,975,493 (Dec. 4, 1990); andBlum et al., German Patent 3,819,942 (Jan. 24, 1990), which areincorporated herein by reference. The molecular weight of the polyamineresin is preferably at least about 200.

Examples of suitable epoxy resins and typical conditions for their useare described in Corcoran, U.S. Pat. No. 4,816,500 (Mar. 28, 1989);Barsotti et al., U.S. Pat. No. 4,906,677 (Mar. 6, 1990); Schimmel, U.S.Pat. No. 4,927,868 (May 22, 1990); Blackburn et al., U.S. Pat. No.4,732,791 (Mar. 22, 1988); Blackburn et al., U.S. Pat. No. 4,755,581(Jul. 5, 1988); Chatta et al., U.S. Pat. No. 4,710,543 (Dec. 1, 1987);Ambrose et al., U.S. Pat. No. 4,749,743 (Jun. 7, 1988) and Tess, "EpoxyResin Coatings", Epoxy Resins Chemistry and Technology, 719-82 (MarcelDekker, Inc. 1988), which are incorporated herein by reference. Theglycidyl component preferably contains at least two glycidyl groups andcan be an oligomer or a polymer. Typical glycidyl components are asfollows: sorbitol polyglycidyl ether, mannitol polyglycidyl ether,pentaerythritol polyglycidyl ether, glycerol polyglycidyl ether, lowmolecular weight epoxy resins such as epoxy resins of epichlorohydrinand bisphenol A, di- and polyglycidyl esters of acids, and polyglycidylethers of isocyanurates. Glycidyl methacrylate or acrylate containingacrylic polymers can be used, such as random and block polymers ofglycidyl methacrylate/butyl methacrylate which are incorporated hereinby reference.

Examples of suitable epoxy resins include resins created by the reactionof epichlorohydrin and related compounds with phenolic compounds such asbisphenols, novolacs, resorcinol, hydroquinone and the like. Othersuitable epoxy resins can be the products of epichlorohydrin withorganic polyacid compounds, such as aliphatic acids (for exampleglutaric, adipic, azeleic acids); cycloaliphatic acids (for examplecyclohexane dicarboxylic acid or cyclohexane tricarboxylic acid);polymerizable acids (such as methacrylic acid); dimerized fatty acids;and aromatic polyacids (for example phthalic, trimellitic andbenzene-tetracarboxylic acids). Other suitable epoxy resins are theproduct of peroxidation of compounds that contain allylic double bondsor internal cyclic double bonds.

The epoxy equivalent weight of the resin (based on 100 percent solids)is preferably at least about 100 and more preferably at least about 130.It is preferably at most about 3000, and more preferably at most about1500. The invention is useful with a broad range of epoxy resins, butthe average molecular weight of the epoxy resin is preferably at leastabout 140 and more preferably at least about 200. The molecular weightis preferably no more than about 10,000.

Polyanhydrides

The present invention also uses polyanhydride resins that contain morethan one pendant, non-cyclic anhydride group linked to a common centralmoiety. The polyanhydride is an asymmetrical anhydride, and preferablycontains a moiety represented by Formula 1(a): ##STR1## wherein (CM) isa central moiety, (R1) is a hydrogen atom or an organic moiety, and n isa number of pendant anhydride groups that averages greater than one.

The central moiety may be a simple organic moiety, such as an aliphatic,cycloaliphatic or aromatic moiety, with a plurality of anhydride groupsbonded to it. Alternatively, it may be a polymer or oligomer thatcontains a plurality of repeating units which are bonded to one or morependant anhydride groups. (As used in this application, the term"polymer" shall include oligomers and copolymers unless otherwisestated.) Examples of suitable non-polymer central moieties includemultivalent phenyl, t-butyl, neopentyl and cyclohexyl structures.Examples of suitable polymeric central moieties include polymers ofstyrene, acrylic and methacrylic acid and their esters, and/or otherethylenically-unsaturated monomers.

The central moiety is linked to more than one non-cyclic anhydridemoiety, on average. It is preferably linked to at least about 2non-cyclic anhydride groups on average and more preferably to at leastabout 3 non-cyclic anhydride groups on average. The anhydride equivalentweight (formula weight per anhydride group) is preferably at least about200 and preferably no more than about 1500.

Each anhydride moiety is typically terminated by a hydrogen atom or anorganic group (R¹). It is preferably terminated by an organic group.This group is preferably aliphatic and more preferably alkyl. Itpreferably contains no more than about 6 carbon atoms, more preferablyno more than about 4 carbon atoms and most preferably no more than about1 carbon atom. The terminating group may also contain a ketone oraldehyde functionality, as in the reaction product of a carboxylic acidand a diketene, which results in an acetoacetic anhydride group.

The anhydride moiety need not be bonded to a polymer or oligomerbackbone. The polyanhydride may optionally contain a polyvalent organicmoiety (A) that is linked to a plurality of anhydride groups by aplurality of pendant linking groups (LG), as illustrated in Formula1(b): ##STR2## The linking group (LG) may contain, for example, esterlinkages, alkylene groups, ether linkages, urethane linkages andcombinations of those. The polyvalent organic group may contain, forexample, a polymer or a polyvalent alkyl or aromatic group. Thecombination of the polyvalent organic moiety (A) and the linking groups(LG) forms the central moiety (CM) as previously described.

The central moiety may optionally contain other functional groups inaddition to the pendant non-cyclic anhydride groups. For example, thecentral moiety may contain pendant acid groups, so that the anhydride isrepresented by Formula 1(c): ##STR3## wherein m is a number of pendantacid groups and all other characters have the meaning previously given.The molar ratio of pendant non-cyclic anhydride groups to pendant acidgroups in the polyanhydride is preferably at least about 25:75, morepreferably at least about 50:50, and more highly preferably at leastabout 75:25. Most preferably, the polyanhydride contains essentially nopendant acid groups.

The central moiety may also contain cyclic anhydride moieties.Preferably, at least 50 percent of the anhydride moieties arenon-cyclic, more preferably at least about 75 percent are non-cyclic,more highly preferably at least about 95 percent are non-cyclic and mostpreferably essentially all are non-cyclic. If the central moiety is apolymer, then the backbone repeating units are preferably not linked byanhydride linkages, like polyanhydrides described in Pettit et al., U.S.Pat. No. 5,055,524 (Oct. 8, 1991), which is incorporated herein byreference. Anhydride linkages between repeating units may also reactduring curing of the resin.

The preferred molecular weight of the polyanhydride varies dependingupon the molecular weight of the coreactant resin. Preferably, if thecoreactant resin is a higher molecular weight resin (average molecularweight of about 2000 to about 10,000), then the polyanhydride resin ispreferably a low molecular weight resin (average molecular weight ofabout 1500 or less). If the coreactant resin is a lower molecular weightresin (average molecular weight of no more than about 2000), then thepolyanhydride resin is preferably a higher molecular weight resin(average molecular weight of about 2000 or greater). Usually, theaverage molecular weight of the polyanhydride resin is preferablybetween about 400 and about 10,000.

Many different polyanhydrides that fall within the broad description canprovide the desired high solids formulations and high exteriordurability of the present invention. However, certain selections ofcentral moiety (CM) and number of pendant anhydride groups (n) arepreferred. The preferred description of the polyanhydride changesdepending upon its molecular weight.

(A) Higher Molecular Weight Anhydrides

When the central moiety is a polymer or oligomer, the number of monomerunits derived from ethylene, propylene and other aliphatic hydrocarbonα-olefins is preferably minimized. Polymers with a high content ofethylene or propylene monomer units do not usually form high solidssolutions in common solvents. The polymer preferably contains no morethan about 50 weight percent aliphatic hydrocarbon monomer units, morepreferably no more than about 25 weight percent, more highly preferablyno more than about 10 weight percent, and most preferably essentiallynone. Monomer units derived from acrylic acid, methacrylic acid andtheir esters provide greater solubility. They preferably make up atleast about 50 weight percent of the polymer and more preferably atleast about 75 weight percent. Polyester polymers also usually have goodsolubility, and so they make good central moieties.

Styrenic monomer units frequently improve the solubility of the polymer,but they may also worsen the exterior durability of the cured coating.The central moiety preferably contains no more than about 25 weightpercent aromatic units, such as are derived from styrene, morepreferably no more than about 20 weight percent, and most preferably nomore than about 15 weight percent aromatic units.

It is theorized that the exterior durability of the cured coating mayalso be improved if the α-carbon atoms which link the anhydride groupsto the central moiety are quaternary carbon atoms, i.e. not bonded to ahydrogen atom. Preferably at least about 50 percent of the α-carbonatoms are quaternary, more preferably at least about 75 percent arequaternary, more highly preferably at least about 90 percent arequaternary and most preferably essentially all are quaternary. Examplesof suitable quaternary α-carbon atoms are set out in Formulae 2(a) and(b): ##STR4## wherein (CM) represents the central moiety and each (R)represents an aliphatic group, which is preferably alkyl and morepreferably lower alkyl (one to six carbon atoms). For instance, thependant linear anhydride groups may be bonded to units derived frommethacrylic acid, rather than to units derived from acrylic acid. Themolecular weight of the central moiety is preferably at least about 1000and more preferably at least about 1500. Examples of processes used tomake high molecular weight anhydrides are described in numerousreferences, such as Maloney, U.S. Pat. No. 3,523,930 (Aug. 11, 1970);Vaughn et al., U.S. Pat. No. 3,631,156 (Dec. 28, 1971); Vaughn, U.S.Pat. No. 3,631,157 (Dec. 28, 1971); Vaughn, U.S. Pat. No. 3,803,087(Apr. 9, 1974); and Vaughn, U.S. Pat. No. 4,308,363 (Dec. 29, 1981),which are incorporated herein by reference. These references teach thatpolyanhydrides can be made by reacting: (a) a polyacid that has morethan two pendant acid groups; with (b) an acylating agent such as ananhydride, an acid halide or a ketene.

The polyacid is preferably highly soluble in at least some commonsolvents, such as hydrocarbon solvents (for example toluene or xylene),chlorinated hydrocarbons, ketones, esters, glycol ethers, polyethers(for instance, glyme or diglyme) or common polar aprotic solvents. Itpreferably forms mixtures in at least one of those solvents at aboutroom temperature that contain at least 50 weight percent solids, morepreferably at least about 60 weight percent and most preferably at leastabout 70 weight percent. Solubility can be measured using any of thosesolvents, but it is conveniently measured in xylene.

Suitable polyacids can be made by several different methods, such as bypolymerization of polymers and copolymers containing acrylic ormethacrylic acid. Many polymers of acrylic and methacrylic acid arecommercially available, and others can be synthesized by well knownprocesses. See, e.g., 1 Encyclopedia Poly. Sci. & Eng. (2d Ed.), Acrylicand Methacrylic Acid Polymers, at 221-224 (J. Wiley & Sons 1985).

(B) Lower Molecular Weight Anhydrides

Lower molecular weight anhydrides preferably contain:

(a) a polyvalent organic moiety (A);

(b) a plurality of ester linkages bonded to the polyvalent organicmoiety;

(c) divalent organic moieties (Q) bonded to the ester linkages; and

(d) non-cyclic anhydride moieties bonded to the divalent organicmoieties.

For example, the lower molecular weight anhydride is preferablyrepresented by Formula 3(a): ##STR5## wherein (A) is the polyvalentorganic moiety, (Q) is the divalent organic moiety, and all othercharacters have the meaning previously described. Of course, thepolyvalent organic moiety (A), the ester linkages and the divalentmoieties (Q) in combination form the central moiety (CM) previouslydescribed. (A) may also contain, or be linked to, other pendant,non-linear anhydride moieties which are not linked by an ester moiety.

The preferred lower molecular weight anhydrides can be made from acorresponding polyacid (see Formula 3(b)), using the sameanhydride-forming reactions that were previously described: ##STR6##

The polyacid can be made by reacting a cyclic anhydride with a polyol.See, e.g., Singer et al., U.S. Pat. No. 4,703,101 (Oct. 27, 1987) andSchimmel et al., U.S. Pat. No. 4,927,868 (May 22, 1990), which areincorporated herein by reference. In the resulting acid, the polyvalentorganic moiety (A) is derived from the polyol, and the divalent organicmoiety (Q) is derived from the cyclic anhydride. Examples of suitablepolyols include phloroglucinol, diresorcinol, glycols, glycerine,trimethylolpropane, pentaerythritol, sorbitol, glucose and/or othersugars. Examples of suitable cyclic anhydrides include maleic, succinic,itaconic, citraconic, glutaric, phthalic and hexahydrophthalicanhydride.

Each (A) and (Q) is preferably aliphatic, aromatic oraliphatic-aromatic. Each aliphatic group is preferably alkyl. Each (A)and (Q) preferably contains no more than about 12 carbon atoms and morepreferably no more than about 7 carbon atoms. On average the centralmoiety is preferably linked to at least about 3 pendant anhydridegroups, and more preferably at least about 4 pendant anhydride groups.On average it is preferably linked to at most about 6 anhydride groupsand more preferably at most about 4 anhydride groups. A highly preferredlower-molecular weight polyanhydride is represented by Formula 3(a)wherein (A) is an aliphatic moiety and (Q) is a cycloaliphatic moiety.The most preferred cycloaliphatic group is a divalent cyclohexane group.The ester and anhydride are preferably in a 1,2-position with respect toeach other. The terminating aliphatic group bonded to the anhydride ispreferably a lower (C₁ -C₆) alkyl group and is most preferably a methylgroup.

The low molecular weight polyanhydride is preferably represented byFormula 4: ##STR7## or a substituted variation thereof, wherein (A) is alower (C₁ -C₆) alkyl group, R is a hydrogen atom or a lower alkyl group,and n is a number of substituent groups averaging greater than 1. n ispreferably about 3 to 4, inclusive. R is most preferably a lower alkylgroup. (A) is preferably a multivalent alkyl group containing about 5 to12 carbon atoms, such as a neopentane group and related alkylstructures. It can be synthesized by: (1) reacting pentaerythritol or arelated polyol with hexahydrophthalic anhydride; and (2) reacting theproduct of that reaction with an acid anhydride (such as aceticanhydride), an acid halide (such as acetyl chloride) or a ketene.

Coating Compositions

Coating compositions of the present invention contain a polyanhydrideand a coreactant resin. They may be applied as powder coatings, but theyare preferably formulated into high solids coating systems dissolved ina solvent or a blend of solvents. The solvent is usually organic.Examples of preferred solvents contain aromatic hydrocarbons, such aspetroleum naphtha or xylenes; ketones, such as methyl amyl ketone,methyl isobutyl ketone, methyl ethyl ketone or acetone; ester solvents,such as butyl acetate or hexyl acetate; or glycol ether esters, such aspropylene glycol monomethyl ether acetate.

The equivalent ratio of the coreactant resin and the polyanhydride resinis preferably at least about 0.8:1, more preferably at least about 0.9:1and most preferably at least about 1:1. The equivalent ratio ispreferably at most about 1.3:1, more preferably at most about 1.2:1 andmost preferably at most about 1.1:1. The polyanhydride and coreactantresin may be partially cured before they are applied to a substrate, butthey preferably are not.

The composition may contain other suitable additions, such as catalysts,pigments, stabilizers, toughening agents and fillers.

It usually contains a catalyst when it is cured. Examples of suitablecatalysts are described in: Smith, U.S. Pat. No. 3,784,583 (Jan. 8,1974); Smith U.S. Pat. No. 3,979,355 (Sep. 7, 1976); Marrion et al.,U.S. Pat. No. 4,452,948 (Jun. 5, 1984); Shalati et al., U.S. Pat. No.4,871,806 (Oct. 3, 1989); Lee & Neville, Handbook of Epoxy Resins 12-13(McGraw-Hill 1967); and Mika & Bauer, Epoxy Resins 487 (Marcel Dekker,Inc. 1988), which are incorporated herein by reference. For example, thecatalyst may be a quaternary phosphonium salt (such astriethylphenyl-phosphonium chloride), a quaternary ammonium salt (suchas tetrabutylammonium bromide), or a tertiary amine (such asdimethylethanolamine. The composition usually contains between 0.1 and 5weight percent catalyst, based upon the weight of solids.

The other materials depend upon its intended use. If the composition isintended for a clear coating, then it preferably does not containfillers, pigments or other materials that can adversely effect theclarity of the cured coating. On the other hand, if it is intended as acolor coating, then it should contain the desired pigments.

The total solids content for a formulation of solvent, coreactant resin,anhydride and other solids in the composition is preferably low enoughso that the viscosity of the composition is within a range that issuitable for its intended use. For instance, the viscosity for anair-spraying composition at 25° C. is preferably at most about 150 cps,more preferably at most about 110 cps, and most preferably at most about70 cps; whereas the viscosity of an airless spraying composition at 25°C. is preferably at most about 5000 cps. The solids content ispreferably at least about 50 weight percent, more preferably at leastabout 65 weight percent, and most preferably at least about 70 weightpercent. The solids content is preferably as high as practical, but itis usually no more than about 95 weight percent (unless the compositionis applied as a powder, in which case it contains about 100 percentsolids).

The composition is applied to a substrate in ordinary ways for coating,such as by conventional spraying, electrostatic spraying, rollercoating, dipping or brushing. It is particularly useful as a clear orcolor coating for outdoor articles, such as automobile and other vehiclebody parts. The substrate may be prepared with a primer and/or a colorcoat or other surface preparation before coating.

The composition becomes a useful thermoset coating by heating at atemperature at which the formulation cures. For most resins, thattemperature is between about 80° C. and about 180° C., although somecoreactant resins can be formulated to cure even at ambient temperature.

The resulting coated article contains a substrate layer and at least onecoating layer that contains a cured composition of the presentinvention. The layer containing the cured composition need not beadhered directly to the substrate; there may optionally be interveninglayers. One preferred coated article system contains:

(a) the substrate;

(b) optionally, a primer or surface treatment layer adhered to thesubstrate;

(c) a color layer adhered either to the substrate or to the primer orsurface treatment layer; and

(d) a clear coat layer adhered to the primer layer,

wherein either the color layer or the clear coat layer contains a curedcomposition of the present invention. The thickness of each layer isdictated primarily by user specifications, and varies depending upon theintended use.

The cured composition preferably has a gloss of at least about 80percent, and more preferably at least about 90 percent, as measured by aBYK MULTIGLOSS multiangle gloss meter at about 20 degrees normal to thesurface. Its distinctness of image is preferably at least about 85 andmore preferably at least about 90, as measured by a DORI-GON D47-6 metermanufactured by Hunter Laboratories. Its exterior durability may betested by coercion "accelerated" test methods such as with a ClevelandQ-Panel QUV unit. The results of such tests (for a UV-stabilizedcoating) are preferably less than 20 percent loss of gloss (measured at20° normal to the panel surface) after 3000 hrs of irradiation at either313 nm or 340 nm.

The compositions of the present invention can easily be formulated withhigh solids content, so that lower quantities of solvent can be used ifdesired. They can be cured to provide coatings with superior exteriordurability.

The invention is further illustrated by the following examples.

ILLUSTRATIVE EXAMPLES

The following examples are for illustrative purposes only. They shouldnot be taken as limiting the scope of either the specification or theclaims. Unless stated otherwise, all parts and percentages are byweight.

EXAMPLE 1 Coating Composition Containing Epoxy Resin and AnhydrideOligomer

Equimolar portions of pentaerythritol and trimethylol propane are placedin a reactor. A blend of 70 percent methylhexahydrophthalic anhydrideand 30 percent hexahydrophthalic anhydride is added in stoichiometricquantities to the reactor. The mixture is heated and stirred at 170° C.until it becomes clear. A mixture of xylenes is added to make an 80percent solids mixture. A catalytic amount of dimethylaminopyridine isadded and the reaction is continued at 135° C. for three hours. The acidequivalent weight is determined by titration with aqueous potassiumhydroxide.

A portion of the mixture containing 10.25 equivalents of acid is dilutedwith xylenes to 60 percent solids. A 1.3× stoichiometric quantity ofacetic anhydride is added and the mixture is stirred for fourteen hours.The pressure is reduced to 300 mmHg and the temperature is increased to60° C. for 2 hours. A 500 g quantity of xylenes is added to maintain anazeotropic distillation of 3 ml/min. over a period of four hours. Afterthe distillation, the reactor is fitted with a Soxhlet extractor thatcontains 3 mol. of anhydrous sodium carbonate. The temperature isincreased to 75° C. and the pressure is reduced slowly to 90 mmHg. The"closed" system is then allowed to reflux for several hours, duringwhich time acetic acid reacts with sodium carbonate in the extractorthimble to an acceptable minimum. The resulting pale yellow resin has aGardner color of 1 and a Brookfield viscosity of 885 cps at 25° C. Itstheoretical anhydride equivalent weight is about 349 at 65.5 percentsolids.

550 parts of the anhydride resin are formulated with 206 partsdiglycidyl cyclohexane dicarboxylate, 6.7 parts quaternary ammoniumcatalyst, 22.2 parts hydroxybenzotriazole UVA, 14.8 parts HALS, 1.5parts flow modifier and 150 parts propylene glycol methyl ether acetate.The mixture is applied by spray at about 63.8 percent solidsconcentration to steel panels precoated with a waterborne white enamelbasecoat. After two minutes flash time, the panels are heated to 135° C.for 30 minutes to cure.

The properties of the cured coating are tested and are set out in Table1.

                  TABLE 1                                                         ______________________________________                                        Test                 Result                                                   ______________________________________                                        MEK double rubs      100+ (no marring)                                        Knoop Hardness       6.6 .sup.+ /.sub.-  0.5                                  Average film thickness                                                                             1.99 mil                                                 Hunter ΔB (yellowness)                                                                       1.2 .sup.+ /.sub.-  8.5%                                 24 hour 5% NaOH      no stain, mar or                                                              erosion                                                  24 hour 5% HCl       no stain, mar or                                                              erosion                                                  20° Gloss     83 .sup.+ /.sub.-  1                                     Distinctness of Image                                                                              87 .sup.+ /.sub.-  1                                     ______________________________________                                    

EXAMPLE 2 Coating Composition Containing Epoxy Resin and AnhydridePolymer

A copolymer containing about 40 weight percent methacrylic acid andabout 60 weight percent butyl acrylate is prepared according to theprocess described in U.S. Pat. No. 4,906,677. A 51 percent solution ofthe resin in a mixture of xylenes, butyl acetate and propylene glycolmonomethylether acetate is heated to 125° C., and the reactor is spargedwith nitrogen to remove volatiles. About 1.1 equivalents of aceticanhydride is added dropwise over about 1.66 hours, and heating iscontinued for another 5 hours. During this time, 100 ml of propyleneglycol methyl ether acetate is added to maintain temperature at 125° C.and 280 ml of acetic acid/solvent azeotrope is recovered. The resultingsolution contains 59.4 percent polyanhydride with an anhydrideequivalent weight of 974 and an acid equivalent weight of 627, asdetermined by titration.

A composition that contains 88.7 parts polyanhydride, 37.0 partsdiglycidyl cyclohexane dicarboxylate, 1.05 parts triethylenediamine and6.9 parts mixed xylenes is formulated. The composition is applied, curedat 121° C. and tested as described in Example 1. The results are set outin Table 2:

                  TABLE 2                                                         ______________________________________                                        Test                Result                                                    ______________________________________                                        MEK double rubs     200+ (no marring)                                         Knoop Hardness      5.2                                                       Average film thickness                                                                            2.56 mm                                                   Hunter ΔB (yellowness)                                                                      1.35 .sup.+ /.sub.-  0.13%                                24 hour 5% NaOH     no stain, mar or                                                              erosion                                                   24 hour 5% HCl      no stain, mar or                                                              erosion                                                   ______________________________________                                    

What is claimed is:
 1. A curable coating composition comprising organicsolvent and:(a) a polyanhydride having a molecular weight of no morethan about 1,500 that contains:(a) a polyvalent organic moiety, (b) aplurality of ester linkages bonded to the polyvalent organic moiety, (c)divalent organic moieties bonded to the ester linkages and (d)non-cyclic anhydride moieties bonded to the divalent organic moieties;(b) an oligomer containing at least two glycidyl groups and having anepoxy equivalent weight of no more than about 1,500; (c) a functionalamount of at least one catalyst; and (d) at least one surfactant orflow-control agent,wherein the composition has a solids content of atleast about 65 weight percent and wherein the eqivalent ratio of epoxyto anhydride is about from 0.8 to 1.3.
 2. The composition of claim 1wherein the active catalyst is selected from the group consisting ofquaternary phosphonium salts, quaternary ammonium salts, and tertiaryamines.
 3. The composition of claim 1 wherein the catalyst is quaternaryphosphonium salt.
 4. The composition of claim 1 wherein the catalyst isphenyltriethylphosphonium chloride.
 5. The composition of claim 1wherein the polyanhydride consists essentially of the reaction productof pentaerythritol, a hexahydrophthalic anhydride and ketene.
 6. Thecomposition of claim 1 wherein the polyanhydride has from 3 to 4pendant, non-cyclic anhydride moieties bonded to each central moiety. 7.The curable coating composition of claim 1 wherein the oligomer isselected from glycidyl ethers of low molecular weight polyols,polyglycidyl esters of polycarboxylic acids, or glycidyl methacrylate orglycidyl acrylate containing acrylic polymers or a mixture of any of theabove.
 8. The composition of claim 1 wherein the oligomer consistsessentially of diglycidyl ester of cyclohexane dicarboxylic acid.
 9. Thecomposition of claim 1 wherein the polyanhydride is preferablyrepresented by the Formula: ##STR8## wherein (A) is a multivalent alkylgroup containing about 5 to 12 carbon atoms, R is a hydrogen atom or aC₁ -C₆ alkyl group, and n is about 3 to 4, inclusive.